Herm Springer Prong Collar

The base neck size for each wire gauge is as follows:
 
1.5mm >
 
2.25mm -> fits up to a 13" neck measurement; designed for use in dogs up to 15- 20 kg
 
3.25mm -> fits up to a 19" neck measurement; designed for use in dogs up to 35 - 45kg
 
4mm > 

If your dog exceeds the starting length capacity of your suggested wire gauge size, you will need to purchase additional middle links